Practicing is a big thing. Obviously, if you don't practice, you will never get better, but if you don't know the proper technique to practice, lots of time with the ball won't help you much either. My advice to you is to get an hour or so in everyday practicing (more if you feel like it) and remember the following...
- Your foot must be FLAT. If you curl your toes up, you're narrowing the contact area and increasing the chance the ball will hit your toes, and screw you up completely. Keep telling yourself in your head to keep your foot straight and flat, and eventually it will click.
- Stand feet shoulder-width apart, for balance.
- Hit on the instep, around the middle of the ball. This will keep the ball from spinning a whole lot, and give you a point to aim for to keep the ball central.
- Use both feet. Being able to do 200 solo juggles with the right foot sucks if you can't do 2 with the left. Try and alternate feet; balance is your friend.
- Juggling is all about timing. Hit it up once, and be patient for the ball to come back down so you can hit it again. If you start bringing your foot to the ball, it's going to go higher, and more out of control, and the juggling will become less natural.
If you remember all that, and keep practicing, you'll become a better juggler. It might take a week to notice any improvement, but it will come... Trust me. Juggling improves touch rapidly. One week your best might be a fluke 10, and the next, you could bag 40. it's all about being consistent and willing to practice.
Have a look at S4L's awesome guide on juggling, for help on how to get started and the benefits of juggling:
See guide here